Propellant composition with a nitro containing cross-linked binder

ABSTRACT

A HIGH ENERGY PROPELLANT COMPOSITION COMPRISING A BINDER, OXIDANT, FUEL AND PLASTICIZER. AN ENERGETIC BINDER FOR SAID COMPOSITION PREPARED BY REACTING A NITRO OR FLUORODINITROMETHYL CONTAINING POLYCARBOXYLIC ACID-DIOL TYPE POLYESTER WITH AN ISOCYANATE OR A CARBOXYL REACTIVE CROSSLINKING AGENT.

U.S. Cl. 149-19 13 Claims ABSTRACT OF THE DISCLOSURE A high energy propellant composition comprising a binder, oxidant, fuel and plasticizer. An energetic binder for said composition prepared by reacting a nitro or fluorodinitromethyl containing polycarboxylic acid-diol type polyester with an isocyanate or a carboxyl reactive crosslinking agent.

This application is a continuation-in-part of application Ser. No. 509,684, filed Nov. 22, 1965, now abandoned.

The invention described herein may be manufactured and used by or for the Government of the United States of America for governemntal purposes without the payment of any royalties thereon or therefor.

This invention pertains to solid propellants and explosives and more particularly to those of the composite type.

One type of solid propellant and explosive which has been used is the so-called composite type and it generally comprises a solid oxidizer, and a solid fuel dispersed in an organic resin. These composites generally suffer from the disadvantage that the polymeric binder is non-energetic thus lowering the total energy content of the system. Some energetic binders based on nitrocellulose-nitroglycerine or nitroplasticized polyurethane have been produced but they are not suitable for many applications because:

(1) They are too sensitive and prone to accidental ignition or explosion.

(2) They are chemically unstable at temperatures above 100 C. or at lower temperatures over longer periods of time.

(3) They have physical properties that change too rapidly with time.

(4) They have poor plasticizer retention.

Accordingly, it is an object of this invention to produce an improved propellant and/ or explosive of the composite type.

It is another object of this invention to produce a binder having a higher total energy content.

It is a further object of this invention to produce a binder with improved plasticizer retention.

-It is still another object of this invention to produce a propellant and/ or explosive with improved mechanical properties.

These and other objects will become more readily apparent from reading the following detailed description of the invention.

The objects of this invention are accomplished by providing a propellant or explosive of the composite type atent O1 3,745,076 Patented July 10, 1973 ice wherein one or more of the components of the resin have energetic substituent groups.

More particularly, the objects of this invention are accomplished by providing a solid propellant or explosive comprising a solid oxidizer, a solid fuel, and a cross-linked polymeric binder having energetic substituent groups as described more fully below, wherein the term cross-linked polymeric binder is used to include both the cross-linked polymeric component and any other conventional propellant or explosive ingredients; e.g., plasticizers, anti-oxidants, wetting agents, polymerization catalysts, reinforcing agents, metal oxides, burning rate catalysts, resonance suppressors, etc., that may be present.

The polymeric component of the binder is generally either a cross-linked polyester or a cross-linked polyurethane, said polymer having energetic substituent groups and being formed from a novel polyester prepolymer having energetic substituent groups. This novel polyester prepolymer is formed by condensing a diol with a polycarboxylic acid wherein either or both components have energetic substituent groups. The diols upon which the energetic groups are substituted are those that are conventionally used for forming polyesters and from among these well known diols there may be mentioned, alkane diols, arene diols, cycloakylene diols, alkane ether diols and the like. Representative compounds include: 2,2-dimethyl-l,3-propanediol; ethylene glycol; tetramethylene glycol; diethylene glycol; hexamethylene glycol; octamethylene glycol; decamethyene glycol; cyclopentylene-l,3-diol; cyclohexylene-1,2-diol; cyclohexylene-l,3-diol; cyclohexylene-l,4- diol; catechol; resorcinol; quinol; l-methyl-2,4-benzenediol; 2-methyl-1,3-naphthalenediol; 2,4-toluenediol; xylylene-1,4-diol; xylylene-1,3-diol; 1,5-naphthalenedimethanol; 2-ethyl-l-phenyl-3-butene-1,2-diol; 2,2 di(4 hydroxyphenyl) propane.

The polycarboxylic acids upon which the energetic groups are substituted are chosen from among those acids conventionally employed for forming polyesters and from among these well-known acids there may be mentioned, alkane diand tri-carboxylic acids, arene diand tri-carboxylic acids, and the like. Representative compounds include, succinic, glutaric, adipic, pimelic, suberic, azelaic, sebacic, phthalic, isopthalic, naphthalenedicarboxylic and trimesic acids. The above acids may also be utilized as their corresponding acid halide or anhydride and when the acid halide is utilized the halogen groups in the polymer may be converted to either carboxyl or hydroxy groups by reaction with either water or a reactive polyol respectively.

The energetic groups utilized for forming the novel polyester prepolymer of this invention are substituted on either the diol, the acid or both the diol and the acid, preferably on the acid. The energetic substituent groups that are generally used are either nitro groups, fluorodinitromethyl groups (F(NO C) or a mixture of these groups, and when nitro is the substituent group there should preferably be at least two nitro groups present on the substituted component. When a diol contains the energetic substituent group, the acidic component is preferably utilized as an acid halide since it is more reactive than its corresponding acid. Thus, in an esterification reaction involving, for example, a diol such as 2,2,8,8-tetranitro-4,6-dioxa-1,9-nonanediol or 2,2-dinitropropanediol improved results were obtained when, for example, 4,4-dinitropimelyl chloride was used instead of 4,4-dinitropimelic acid.

It is generally desirable to introduce some branching into the polyester and for this purpose a polyfunctional alcohol may be employed in admixture with the diol. The polyfunctional alcohol employed is one of those generally utilized for forming branched polyesters and from among these well known alcohols there may be mentioned, glycerol, trimethylolpropane, trimethylolethane, mannitol, pentaerythritol, and the like. It is to be understood that the above mentioned diols, polybasic acids, and polyfunctional alcohols may be used either singularly or in combination with other diols, polybasic acids and polyfunctional alcohols, respectively.

The polyester prepolymer preferably has a molecular weight between about 2500 and 6000 and it is formed by a condensation reaction of the type generally employed for forming polyesters; e.g., condensation in the presence of an acid catalyst such as p-toluene sulfonic acid. Since these reactions are well known in the art, their details will not be set forth herein.

If the polymeric binder is to be of the polyester type, an excess of acid is utilized thereby introducing carboxyl groups into the polyester. The polyester is then crosslinked with a carboxyl reactive cross-linking agent of the type generally employed for cross-linking polyesters containing carboxyl groups; i.e., compounds that have groups that are reactive with carboxyl groups. The cross-linking agent is generally used in excess of the amount which is equivalent stoichiometrically to the number of carboxyl groups present, ranging upwards from about to 100% greater, and preferably -40% greater. The cross-linking agent employed is preferably a polyimine or a polyepoxide; e.g., the diglycidyl ether of bis-phenol A sold under the name *Epirez 510, the diglycidyl ether of bisphenol F [diglycidyl ether of bis-(4-hydroxyphenyl) methane], tri l-(2-methyl) aziridinyl phosphine oxide sold under the trade name MA'PO, the triglycidal ether of trihydroxydiphenyl sold under th'e trade name of Kopax 171, and the like. The polyimine compounds that are operable as cross-linking agents in this invention are described in more detail in Pat. No. 3,182,041, granted on May 4, 1965, said disclosure of aziridines being hereby incorporated by reference. If an epoxy compound is used as the cross-linking agent it is preferred to use a catalyst of the type generally employed for accelerating carboxy-epoxy reactions. It was found that good results were obtained with ferric compounds, e.g. ferric acetylacetonate, ferric soaps, ferric chloride hexahydrate, and the like.

If the polymeric binder is to be of the polyurethane type, an excess of diol is utilized thereby introducing hydroxy groups into the energetic polyester. The polyureethane of the binder is the reaction product of; (a) an energetic polyester prepolymer containing hydroxy groups of the type described above; (b) an organic compound having as its sole reacting groups, two isocyanate groups; and (c) an isocyanate reactive cross-linking agent, with the diisocyanate being used in at least a stoichiometric amount (based on the active hydrogen functionality of the polymeric component and cross-linking agent), with an excess up to being preferred. The ratio of polyester to cross-linking agent will vary depending upon the degree of cure desired, said ratio based on equivalents) generally varying between 1 to l and l to 2.

The diisocyanate utilized may be chosen from any one of a wide variety of organic diisocyanates which are generally employed for forming polyurethanes, including saturated and unsaturated; aliphatic or aromatic; open or closed chain; and if the latter, monocyclic or polycyclic; diisocyanates. The diisocyanates may or may not be substituted with groups that are substantially unreactive with isocyanate or hydroxyl groups, such as; for example, ketone, halogen, ester, sulfide, ether or nitro groups. Representative examples of diisocyanates which are operable in this invention are given in Pat. No. 3,132,976, granted May 12, 1964, which is hereby incorporated by reference.

The cross-linking agents which are used either singularly or in combination with each other in forming the cross-linked polyurethane binder of this invention are chosen from among the wide variety of polyfunctional compounds employed for cross-linking polyurethanes. The cross-linking agents utilized are preferably non-basic in order to prevent any possible interaction with the plasticizer with compounds having as their sole reacting groups, three or more groups capable of reacting with isocyanate groups, e.g., groups containing active hydrogen being particularly effective. It is to be understood that these compounds may also contain groups that are relatively unreactive with isocyanate or hydroxy groups such as, for example, ketone, halogen, ester, sulfide or ether groups and the term sole reacting groups is not meant to exclude these groups. Representative compounds include: saturated aliphatic and aromatic polyhydric alcohols, such as l,2,3-prop-anetriol (glycerol), 1,2,6-hexanetriol, trimethylolpropane, erythritol, pentaerythritol, rabitol, xylitol, sorbitol, mannitol, trimethylolphenol, trimethylolbenzene, and the like, esters of polyhydric alcohols and fatty acids, such as castor oil, glyceryl mono-, di-, and triricinoleate, glyceryl mono-, di-, and tri(12- hydroxystearate), pentaerythritol mono-, di-, tri-, and tetraricinoleate, pentaerythritol mono-, di-, tri-, and tetra(12 hydroxystearate), 2,3 dihydroxypropyl- 12-hydroxystearate, 2,3-dihydroxy ricinoleate, and the like; alkylene oxide adducts of polyhydric alcohols, such as ethylene oxide adducts of glycerol, 1,2,6-hexanetriol, and pentaerythritol, propylene oxide adducts of glycerol (NlAX Triol LG Series) propylene oxide adducts of 1,2,6-hexanetriol, (NIAX Triol LHT Series), and the like; condensation products of 2 or more polyhydric alcohols, such as condensation products of 1,2,6-hexanetriol and glycerol; and the like; polyhydric derivatives of sugars, such as the octakis(2-hydroxypropyl) derivative of sucrose (Hyprose 'SP80), and the like derivatives of glycose; and the like.

It is also generally desirable to employ a polymerization catalyst of the type generally used in the polymerization of polyurethanes. As representative examples of these well-known catalysts there may be mentioned the organometals such as ferric acetylacetonate, dibutyl tin diacetate, titanyl acetylacetonate, vanadyl acetylacetonate, and the like.

The binders of this invention also include a high energy plasticizer in order to increase the total energy of the binder system. As representative examples of these plasticizers there may be mentioned, nitro compounds such as the bis(dinitroalkyl acetals); e.g., the bis(dinitropropyl) acetal of formaldehyde, the bis(dinitropropyl) acetal of acetaldehyde, etc.), etc.; nitrato compounds such as triethyleneglycol dinitrate, diethyleneglycol dinitrate, nitroglycerine, etc.; fiuorodinitromethyl compounds such as bis(2-fiuoro-2,2-dinitroethyl) formal (FEFO), etc.; and the like. These plasticizers are generally employed in weight ratios up to about 3.5 to 1 based on the weight of the polymeric component of the binder, with the upper ratios of plasticizer to hinder being intended for explosive uses and the lower ratios for propellant uses. The nitro and fluorodinitromethyl plasticizers are described in more detail in application Ser. No. 173,592 filed on Feb. 15, 1962, now US. Pat. No. 3,526,667, and assigned to the same interest, said application hereby being incorporated by reference.

The solid salts which are used either singularly or in combination with each other as the oxidizer, are employed in powdered form (average particle sizes usually range between 1 and 300 microns) and they representatively include the nitrates, perchlorates, chlorates, permanganates, chromates and dichromates of the alkali or alkaline earth metals; ammonia; hydrazine, or guanidine. As representative compounds there may be mentioned, ammonium nitrate, ammonium perchlorate, sodium nitrate, potassium perchlorate, lithium chlorate, calcium nitrate, barium perchlorate, strontium chlorate, and the like, with ammonium perchlorate being preferred. The oxidizer to binder weight ratio generally employed ranges from about 0.8 to 1 to about 18 to 1, preferably between about 1.1 to 1 and 2.4 to 1.

The binder also includes a solid fuel component in powdered form (average particle size usually ranges from about 1 to 200 microns) and from among the well-known solid fuels there may be mentioned metals such as, aluminum, boron, magnesium, beryllium, etc.; metal alloys such as, the aluminum alloys of boron, magnesium, manganese, zinc, copper, etc.; metal hydrides such as, the hydrides of aluminum, beryllium, etc.; and the like. These solid fuels are generally employed in weight ratios ranging from about .04 to 1 to about 7 to 1 based on the weight of the binder and preferably between about 0.4 to 1 and 1 to 1.

The binder may include, as "mentioned above,"conven-" tional ingredients such as antioxidants; e.g., BLE (reaction product of acetone and diphenylamine) etc.; wetting agents; e.g., lecithin, etc.; metal oxides; e.g., magnesium oxide, etc.; reinforcing agents; e.g., lignin, etc.; burning rate catalysts; e.g., copper chromite, etc.; resonance suppressors; e.g., carbon black, etc.; and the like. These additives generally do not comprise more than about 10% p of the composition.

It is to be understood that the above mentioned specific examples of alcohols, acids, diisocyanates, crosslinking agents, solid oxidizers, solid fuels, etc., are only representative examples of the wide variety of these compounds which may be utilized in this invention and they are not to be construed as limiting the invention in any manner.

As an alternative embodimnt to the explosive described above comprising an oxidizer, a fuel and the upper weight ratio of plasticizer to binder, an explosive may be prepared by replacing the oxidizer and fuel with an explosive such as TNT, RDX, HMX and the like. The explosive is dispersed in the crosslinked energtic polymeric binder and it is generally employed in weight ratios ranging from about 2.4 to 1 to about 19 to 1 based on the energetic binder. This explosive may be produced by either casting or pressing.

The composite propellant or explosive is generally prepared by blending all ingredients under vacuum until a homogeneous slurry is formed. The resulting mixture is cast and cured (generally between about 60 and 200 F.) into a solid propellant or explosive comprising solid components dispersed in a resinous fuel binder. Alternatively, if a propellant is formed, it can be cast and cured directly in a rocket chamber lined with an inert liner material.

The following examples are illustrative of the invention but its scope is not to be limited thereby.

EXAMPLE I 10.5 moles of 4,4-dinitropimelic acid, 8.5 moles of diethylene glycol, and 0.5 mole of trimethylol propane were placed in a resin kettle fitted with a stirrer, water separator and thermometer along with one liter of toluene per 1000 girls. of reactant and a p-toluene sulfonic acid catalyst (0.5% by weight). The mixture was heated at reflux with stirring until water evolution stopped. The solvent was removed and a polyester containing carboxyl groups having a molecular weight of about 5500 was recovered.

EXAMPLE II 0.94 mole of 4,4-dinitropimelic acid and 1.00 mole of diethylene glycol were placed in the resin kettle along with one liter of toluene per 1000 grns. of reactants and a p-toluene sulfonic acid catalyst (0.5% by wt). After heating at reflux and removal of the solvent a polyester containing hydroxy-groups having a molecular weight of about 5500 was recovered.

6 EXAMPLE m 0.02 mole (6.88 g.) of 2,2,8,8-tetranitro-4,6-dioxa-1,9- nonanediol and 0.025 mole (7.175 g.) of 4,4-dinitropimelyl chloride were hand stirred together in a small glass reactor placed in an oil bath. When the temperature reached 6070, the reactants melted to a clear liquid and as the temperature was raised further to -130" the evolution of hydrogen chloride began. The hydrogen chloride evolved was measured by titration with base and after about 2.5 hours at this temperature about 96% of the theoretical quantity of hydrogen chloride had been evolved. During this time the viscosity of the melt continually increased until at the end of the reaction a thick, syrupy liquid was obtained which set to a tacky glass if cooled.

At this point, g. of bis(2-fiuoro-2,2-dinitroethyl) formal (FEFO) was added to reduce the viscosity of the prepolymer (FEFO also acts as a plasticizer for the cured polymer). Then the residual acid chloride end groups were esterified by adding 0.01 mole (1.34 g.) of trimethylol propane to the melt at about 100. The mixture was stirred while heating at 100 until the evolution of hydrogen chloride ceased. At this point, the prepolymer was pumped for about 20 min. at about 5 mm. while heated, to out-gas any entrapped hydrogen chloride. When cooled, the prepolymer containing about 50% by weight of FEFO, was a colorless, waxy solid.

EXAMPLE IV A typical curing procedure using a diisocyanate was carried out by taking 5.41 g. of the prepolymer of Example III containing 50% by weight of FEFO 'and thoroughly mixing in 0.34 g. of hexamethylene diisocyanate and about 10 mg. of 4,4-dinitropimelic acid as a curing catalyst while warming the mixture at about 80. After the mixture was homogeneous, it was pumped in vacuo at 65 to remove any residual gases and then cured at 65 for 18 hours. The product was a rubbery solid with fair tensile strength and elongation. When ignited, it burned at a uniform rate.

EXAMPLE V A propellant was prepared from the following composition:

a homogeneous slurry was formed. The mixture was cast in a container and cured to a rubbery solid by heating at 6070 C. for 24 to 48 hours.

The propellant had the following properties:

Density (gm./cm. 1.80 Max. tensile strength (p.s.i.) 75 Elongation (percent) 70 Burning rate at 1000 p.s.i. (in/sec.) 0.36 Isp (theoretical), sec. 264

EXAMPLE VI An explosive can be made similarly to the procedure for forming the propellant of Example V by increasing the energetic plasticizer to polymeric component ratio.

The following composition was-cast and cured to a solid explosive by using the procedure of ExampleV.

Ingredient: Weight percent Ammonium perchlorate 38.0 Aluminum 25.5 FEFO 28.0 Polyester of Example I 7.0 Kopox 171 1.3 Ferric acetylacetonate 0.2

' degradation and improved plasticizer retention. The propellants, due to their higher impulse characteristics will be used in a wide variety of rockets. The explosives produced by this invention may be utilized as sheet explosives, in delayed detonation bombs, and as a heat resistant missile explosive.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood, that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. A composition capable of being cast and cured comprising:

(a) a polyester, said polyester being selected from the group consisting of polyesters containing carboxyl groups and polyesters containing hydroxy groups, said polyester containing energetic substituent groups, said energetic substituent groups being selected from the group consisting of nitro, fluorodinitromethyl, and mixtures of nitro and fluorodinitromethyl groups, said polyester being the reaction product of a composition comprising (1) a diol selected from the group consisting of alkane diols, arene diols, cycloalkylene diols and alkane ether diols, and (2) a member selected from the group consisting of polycarboxylic acids selected from the group consisting of alkane dicarboxylic acids, alkane-tricarboxylic acids, arene dicarboxylic acids, arene tricarboxylic acids, their corresponding acid halides and their corresponding acid anhydrides, at least one of said components (1) and (2) being substituted with the energetic group;

(b) a member selected from the group consisting of 1) carboxyl reactive cross-linking agents and (2) a mixture of a diisocyanate organic compound and an isocyanate reactive cross-linking agent,

(c) a member selected from the group consisting of a solid explosive and a mixture of a solid oxidizer and a solid fuel; and

(d) a high energy plasticizer.

2. The composition of claim 1 wherein component (a) is a nitro-substituted polyester containing carboxyl groups, said polyester being the reaction product of a composition comprising a diol and a dicarboxylic acid containing at least two nitro groups and component (b) is a crosslinking agent capable of reacting with carboxyl groups.

3. The composition of claim 1 wherein said nitro substituted polyester containing carboxyl groups is a branched polyester, said polyester being the reaction product of a composition comprising a diol, a polyfunctional alcohol and a dicarboxylic acid containing at least two nitro groups.

4. The composition of claim 1 wherein said nitro sub- 8 stituted polyester containing carboxyl groups is the reaction product of a composition comprisin 4,4-dinitropimelic acid and diethylene glycol.

5. The composition of claim 1 wherein said high energy plasticizer is selected from the group consisting of nitrate, nitro and fluorodinitromethyl plasticizers.

6. The composition of claim 1 wherein component (a) is a nitro substituted polyester containing hydroxy groups, said polyester being the reaction product of a composition comprising a diol and a dicarboxylic acid containing at least two nitro groups and said component (b) is a mixture of an organic compound having as its sole reacting group two isocyanate groups and a cross-linking agent capable of reacting with isocyanate groups.

7. The composition of claim 6 wherein said plasticizer is selected from the group consisting of nitro, nitrate and fiuorodinitromethyl plasticizers.

8. The composition of claim 7 wherein said nitro substituted polyester containing hydroxy groups, is the reaction product of a composition comprising diethylene glycol and 4,4-dinitropimelic acid.

9. The composition of claim 1 wherein component (a) is the reaction product of a composition comprising (1) 2,2,8,8tetranitro-4,6-dioxa-1,9-nonanediol and (2) 4,4- dinitropimelyl chloride.

10. The composition of claim 1 wherein component (a) is the reaction product of a composition comprising (1) 2,2-dinitropropanediol and (2) 4,4-dinitropimelyl chloride.

11. A high energy composite comprising:

(a) a binder comprising a cross-linked polymer and a high energy plasticizer, said crosslinked polymer containing energetic substituent groups selected from the group consisting of nitro, fluorodinitromethyl, and mixtures of nitro and fluorodinitromethyl groups,

' said crosslinked polymer containing energetic substituent groups being selected from the group consisting of a cross-linked polyester and a cross-linked polyurethane wherein said polyester containing said energetic groups is the reaction product of a composition comprising (1) a diol selected from the group consisting of alkane diols, arene diols, cycloalkylene diols and alkane ether diols, and (2) a member selected from the group consisting of a polycarboxylic acid selected from the group consisting of alkane dicarboxylic acids, alkane-tricarboxylic acids, arene dicarboxylic acids, arene tricarboxylic acids, their corresponding acid halides and their corresponding acid anhydrides, at least one of said components (1) and (2) being substituted with the energetic substituent group and said polyurethane containing said energetic groups is the reaction product of an organic compound containing as its sole reacting groups two isocyanate groups and a polyester containing hydroxy groups wherein said hydroxy containing polyester is the reaction product of a composition comprising (3) a diol selected from the group consisting of alkane diols, arene diols, cycloalkylene diols and alkane ether diols, and (4) a member selected from the group consisting of polycarboxylic acids selected from the group consisting of alkane dicarboxylic acids, alkane-tricarboxylic acids, arene dicarboxylic acids, arene tricarboxylic acids, their corresponding acid halides and their corresponding acid anhydrides, at least one of said components (3) and (4) containing said energetic substituent group; and

(b) a member selected from the group consisting of an explosive and a mixture of a solid fuel and a solid oxidizer said member being dispersed in said binder wherein when said member is a solid explosive the weight ratio of explosive to binder ranges between is bis(2-fluoro-2,2-dinitroethyl) formal, said nitro sub- 10 sti'tuted polyester is the reaction product of a composition comprising 4,4-dinitropimelic acid and diethylene glycol, said solid fuel is aluminum, and said solid oxidizer is ammonium perchlorate.

10 References Cited UNITED STATES PATENTS 3,242,139 3/1966 Long et al. 260-644 X 3,255,059 6/1966 Hamermesh et a1. 14919 3,256,214 6/1966 Bluhm 149-19 X FOREIGN PATENTS 928,920 7/ 1963 Great Britain 149-88 949,086 2/1964 Great Britain 149-19 LELAND A. SEBASTIAN, Primary Examiner US. Cl. X.R. 

